1. Field of the Invention
The invention relates to driving a CCFL (cold cathode fluorescent lamp) with a high voltage sine wave to produce an efficient and cost effective light source. This light source can be used for backlighting in applications including, but not limited to, a notebook computer, a flat panel display, and a personal digital assistant (PDA).
2. Discussion of the Related Art
Fluorescent lamps are being used in an increasing number of applications. These applications include backlighting for many consumer products including, for example, notebook computers, flat panel displays, and personal digital assistants (PDAs). One common type of fluorescent lamp is a cold cathode fluorescent lamp (CCFL). A CCFL tube contains a gas, which is ionized to generate the desired light for the application.
During standard operation, CCFL tubes typically require a sine wave of 600 V and run at a current of several milliamps. However, the starting (or striking) voltage of the CCFL tube, which is used to ionize its contained gas, can be as high as 2000 V. At start up, the CCFL tube looks like an open circuit, i.e. the impedance of the CCFL tube prevents any current. However, after the gas is ionized, the impedance drops and current starts to flow in the CCFL tube.
In typical embodiments, the CCFL tube is driven by a high Q circuit, wherein Q refers to the quality of the circuit and is measured by the inductive or capacitive reactance of the circuit at resonance divided by the resistance. This high Q circuit generally includes additional capacitors and inductors, which undesirably increase the number of components in the system. Therefore, a need arises for a CCFL circuit that minimizes the number of additional components while still achieving an efficiency of at least 85%.